Transformers worksheet with answers

Free printable Transformers worksheet: 6 problems from easy to exam level, with an answer key. Print it or save it as a PDF.

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1.Easy

An ideal transformer must step 960 V down to 240 V. Its primary winding has 240 turns. How many turns N₂ does the secondary winding need?

V₁ = 960 VV₂ = 240 VN₁ = 240

N₂ =

2.Easy

An ideal transformer has 100 turns on its primary winding and 800 turns on its secondary winding. The primary is connected to a 230 V AC supply. Find the secondary voltage V₂.

N₁ = 100N₂ = 800V₁ = 230 V

V₂ = V

3.Medium

An 8 Ω resistor is connected across the secondary winding of an ideal transformer with a turns ratio N₁:N₂ = 12:1. Find the resistance R_1′ seen looking into the primary winding.

N₁:N₂ = 12:1R_L = 8 Ω

R_1′ = Ω

4.Medium

An amplifier with an output resistance of 1200 Ω drives a 75 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 1200 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

R_s = 1200 ΩR_L = 75 Ω

a =

5.Hard

A single-phase 75 kVA transformer has a core loss of 450 W and a copper loss of 1350 W at rated load. It supplies 50% of its rated kVA at a power factor of 0.85 lagging. Find the total losses P_loss in watts at this load.

S = 75 kVAP_core = 450 WP_cu,fl = 1350 Wx = 0.5pf = 0.85

P_loss = W

6.Hard

A single-phase 75 kVA transformer has a core loss of 375 W and a copper loss of 1500 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 75 kVAP_core = 375 WP_cu,fl = 1500 W

S_η,max = kVA

Answer key

1. N₂ = 60
2. V₂ = 1840 V
3. R_1′ = 1152 Ω
4. a = 4
5. P_loss = 787.5 W
6. S_η,max = 37.5 kVA

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